With a recent trend of mobile equipment increasingly becoming higher in performance and smaller in size, electronic circuit devices are required to be larger in memory capacity, higher in performance, and smaller in size. Accordingly, there is a strong demand for high-density mounting based on finer and narrower pitch wiring rules for semiconductor elements.
Conventionally, flip-chip mounting technology is available as a technology for high-density mounting of electronic components such as semiconductor elements on various wiring boards.
In ordinary flip-chip mounting, for example, a solder bump of about 100 μm in diameter is formed on an electrode terminal of a semiconductor element such as LSI. After that, the semiconductor element is press-fitted and heated to connect the bump to a connector terminal of the mounting substrate by a face-down bonding method.
However, in such a mounting technology with use of a solder bump, a high pressing force is required for press-fitting in the mounting step, causing a great load to be applied to the semiconductor element. Therefore, in the case of recently available semiconductor element reduced in size having Low-K dielectric layer, there arises a problem such as breakdown of fragile dielectric layer, element breakage, or variation of semiconductor element characteristics.
As a technology for solving the above problem, a semiconductor device with a stress absorbing ball formed of polymer ball having a conductive member on the surface thereof arranged between an electrode terminal of the semiconductor element and a connector terminal of the wiring board and with a conductive member connected to the electrode terminal and connector terminal by diffusion bonding is disclosed (for example, refer to Patent document 1). In this way, connection trouble can be decreased because stresses generated in the press-fitting and heating step are absorbed by the stress absorbing ball, and electrical resistance can be reduced by diffusion bonding.
On the other hand, a method of exposing and developing a predetermined portion of a semiconductor element coated with solder particle photosensitive resin that is photosensitive resin containing solder particles is disclosed as a method of forming a solder bump (for example, refer to Patent document 2). In this way, a solder bump with solder particles diffused in the resin can be formed with excellent productivity. Also, bump connection can be performed by pressing the semiconductor element against the wiring board by means of a clamp.
However, in the semiconductor device of Patent document 1, there arises such a problem that the manufacturing cost becomes higher for forming a smaller-sized stress absorbing ball having a conductive member on the surface thereof. Also, a bump electrode is formed by arranging a small-sized stress absorbing ball on the electrode terminal, and in this method, it is difficult to make the arrangement corresponding to the size reduced, making it difficult to realize high-density mounting.
Also, in the solder bump forming method of Patent document 2, since it is a mounting structure such that contact connection is made by pressing the solder bump having solder particles diffused in the resin and solder particles contacting with each other, there arises a problem such as generation of great electrical resistance and worsening of connection reliability.    Patent document 1: Unexamined Japanese Patent Publication H5-21519    Patent document 2: Unexamined Japanese Patent Publication H5-326524.